758 NEW YORK STATE MUSEUM 



PLATE 6 



Genus goniograptus McCoy 



See pi. 7 



Goniograptus thureaui McCoy var. postremus yar. nov. 



Page 621 



1-11 Astogenetic growth stages 



1 Young rhabdosome consisting of sicula and first two thecae. xS^ 



2 Young rhabdosome, in which the branches of the first oriler have bifurcated, 



seen from the obverse side. xS^ 



3 A like growth stage seen from the reverse side. x3^ 



4 The next stage, in which the eight branches of the third order have 



formed. x3^ 



5 A slightly more advanced stage from the reverse side. The brachial 



thecae of the " denticulate branches " have commenced to form. 

 x3i 



6 A similar growth stage seen from the obverse side. xS^ 



7 A further growth stage of the rhabdosome, possessing the branches of the 



fourth order and short denticulate branches. x2| 



8 Rhabdosome in an adolescent growth stage, in which the formation of the 



branches has proceeded to that of the eighth order and further growth 

 consists in the lengthening of the denticulate branches. x2^ 



9 A somewhat more advanced growth stage showing the further longitudinal 



growth of the branches. x2^ 



10 A rhabdosome in which the formation of new branches has ceased, showing 



well the arrangement of the branches and the character of the four 

 principal stems 



11 Mature rhabdosome 



12 Central portion of a mature rhabdosome retaining the alate central 



disk. x2 



13 A fragment of a rhabdosome. x2 



